1. Field of the Invention
The present invention relates to a movement vector detecting device, and more particularly to a device for detecting a movement vector from an image signal.
2. Related Background Art
The movement vector detecting device has been employed in the image encoding device or the image vibration compensating device. For movement vector detection by image signal processing, there have been known a time-space inclination method disclosed for example in the U.S. Pat. No. 3,890,462 and in the Japanese Patent Publication No. 60-46878, a correlation method based on calculation of correlation, and a block matching method.
In the time-space inclination method, the amount of movement is calculated from the difference d in luminance between frames (or fields) and the difference xcex94 between pixels in a frame. There is utilized a property that the image signal of a moving image is an average in time with a field cycle time, and that the edge becomes less sharp and the difference xcex94 in luminance among pixels becomes smaller as the amount of movement of image becomes larger. The amount of movement is defined by d/xcex94, namely the difference d in luminance among frames or fields, normalized by the difference xcex94 in luminance among pixels. The details of the time-space inclination method are described by B. K. P. Horn et al., Artificial Intelligence 17, p.185-203 (1981).
The block matching method consists of dividing the input image signal into blocks of a suitable size (for example 8 pixels by 8 lines), comparing each block with the pixels of a predetermined area in a preceding frame (or field) and determining the most resembling position by laterally moving the comparing position within the image frame. For example there is searched a position where the sum, within the block, of absolute difference of pixels between the frames (or fields), and the movement vector is represented by the relative displacement of the most resembling blocks. The details of the block matching calculation are reported by M. Ogami et al., Information Processing, Vol. 17, No. 7, p.634-640 July, 1976.
In these methods, however, it has been difficult to exactly detect the movement vector, or the detected movement vector has not been reliable, in case the unit block for movement vector detection contains only low spatial frequencies and lacks characteristic pattern (such as sky, water surface, white wall or asphalt surface), or in case said unit block contains a plurality of similar characteristic points with a high spatial frequency (such as flower field, leaves of a tree or a door with grid pattern), or in case an object having the edge only in a specified direction (such as an oblong rod) moves along the direction of said edge.
If a high-efficiency image encoding device or an image vibration compensating device is operated according to an erroneous movement vector or a movement vector involving a large error, the precision of encoding or compensation is significantly deteriorated, and the image quality may become even worse by such encoding or compensation.
In the field of vibration detection and vibration compensation utilizing the movement vector, the present applicant already has following patent applications and patents:
U.S. patent application Ser. Nos. 07/925,247, 07/935,633, 07/896,783, 07/852,494, 07/967,569, 07/691,784, 07/983,277, 07/799,053 and 07/798,946;
U.S. patent application Ser. No. 07/880,512 filed Jun. 30, 1986 and Ser. No. 07/425,477 filed Oct. 23, 1989; and
U.S. Pat. Nos. 5,012,270 and 5,107,293.
The present invention is to resolve the above-mentioned drawbacks of the prior art, and a first object thereof is to provide a movement vector detecting device capable of exactly detecting the movement regardless of the state of the image.
A second object of the present invention is to provide a vibration compensating device capable of exactly detecting the movement vector of an object image regardless of the pattern thereof, and enabling to realize optimum movement compensating characteristics without erroneous operations.
A third object of the present invention is to provide a camera constantly capable of exact compensation for vibration regardless of the state of the object to be photographed.
The above-mentioned objects can be attained, according to a preferred embodiment of the present invention, by a movement vector detecting device comprising movement vector detecting means for dividing the image frame into plural blocks and detecting the movement vector in each block; edge detecting means for detecting the number of edges of the image in each block; and evaluation means for evaluating the reliability of the movement vector value detected by said movement vector detecting means, based on the number of edges detected by said edge detecting means.
Also according to another aspect of the present invention, there is disclosed a vibration compensating device comprising movement vector detecting means for dividing the image frame into plural blocks and detecting the movement vector in each block; edge detecting means for detecting the number of edges of the image in each of said blocks; calculation means for varying the weight on the movement vector value detected by said movement vector detecting means, based on the number of edges detected by said edge detecting means, thereby calculating the movement vector evaluation value of the image, and compensation means for compensating the image movement based on the output of said calculation means.
As the detected movement vector values of low reliability, based on the number of edges, are evaluated lightly or are excluded, it is rendered possible to obtain the exact movement vector values of high reliability in appropriate areas, and to constantly effect optimum detection of vibration.